Apparatus for comparing two dimensions

ABSTRACT

An apparatus is provided for storing a voltage corresponding to one dimension, for storing a second voltage corresponding to a second dimension, for comparing two voltages, and for indicating whether the difference between the two voltages is within an acceptable range. Such an apparatus can be used to indicate whether the maximum and the minimum diameters of a round object are close enough in value for the round object to be acceptable for use in applications where perfect roundness is desirable.

United States Patent i 13,593,133

[72] inventor Daniel A. Wlsner [56] References Cited D M UNITED STATESPATENTS P 1 2,468,687 4/1949 Schmitt 324/111 x [221 FM 3,371,419 3/1968Banks et a]. 1. 33/174 [45] F My 3,132,307 5/1964 Augustine m1. 330/69 x[731 RCA 3,131,350 5/1965 Thomas et a1. 324/103 x 3,277,312 10/1966Harris 330/69 X Primary Examiner-Rudolph V. Rolinec AssistantExaminer-Ernest F. Karlsen v Attorney-Edward J. Norton [541 APPARATUSFOR COMPARING TWO DIMENSIONS ABSTRACT: An apparatus is provided forstoring a voltage 4 Claims 1 Drawing corresponding to one dimension, forstoring a second voltage [52] 11.8. C1 324/103 R, corresponding to asecond n i f r omp ring o vol 33/174 Q, 324/140R ages, and forindicating whether the difference between the [51] Int. Cl ..G0lr 19/16,two o tages is ithin an acceptable range. Such an apparatus 601; 7/00can be used to indicate whether the maximum and the [50] Field olSearch324/111, minimum diameters of a round object are close n g in 103, 103P, 140; 328/ 135, l 16, 147, 148; 340/248, value for the round object tobe acceptable for use in applical72, 271, 267; 33/174 Q; 330/69, 30 Dtions where perfect roundness is desirable.

APPARATUS FOR COMPARING TWO DIMENSIONS BACKGROUND A completed round orcylindrical object may not be perfectly round and, in fact, somethingless than perfect roundness may be acceptable for the purpose for whichthe round or cylindrical object has been made. However, the degree ofoutof-roundness, that is the difference between the maximum and theminimum diameter, of the object must not exceed a predetermined amountif the machine in or with which the object to be used is to operatesatisfactorily. Manual inspection of each object is slow and expensive.

It is an object of this invention to provide an improved apparatus forcomparing two dimensions.

It is a further object of this invention to provide improved apparatusto indicate when the difference between two dimensions are greater orless than a p Jetermined amount.

It is a still further object of this invent on to provide improvedapparatus for indicating out-of-roundness of a cylindrical object.

SUMMARY In accordance with the invention, two voltages are stored, themagnitude of one voltage being a measure of the greater of the twodimensions to be compared and the magnitude of the other voltage being ameasure of the smaller of the two dimensions to be compared. These twovoltages are applied to a voltage comparison means and the output of thevoltage comparison means is applied to a threshold detector whichindicates whether the difference between the two stored voltages, andtherefore the difference between the two corresponding dimensions, arewithin or outside of a predetermined amount. lf the two dimensions to becompared are the maximum and minimum diameter of a round object such asa cylinder, the cylinder is rotated about its axis and a voltage isstored which is a measure of the maximum diameter of the cylinder andanother voltage is stored which is a measure of the minimum diameter ofthe cylinder, these two voltages being applied to the voltage comparisonmeans.

The invention will be better understood upon reading the followingdescription in connection with the accompanying drawing which comprisesa single FIGURE illustrating, partially in block form, an apparatusincluding one embodiment of the invention.

Let it be assumed that the two dimensions to be compared are the maximumand minimum diameters of a cylinder 10. The cylinder is mounted forrotation on a shaft lll about its axis by apparatus not shown. Aninsulating feeler 112 of a dimension sensing means 14 is placed incontact with the surface of the cylinder 10. The dimension sensing means14 comprises a conductive housing 16, there being a hole l8 through onewall of the housing l6, the insulating rod 12 extending through the hole18. The inner end of the rod R2 is attached to a conductive capacitorplate 22. An inductance coil 24 is connected between the plate 22 andground 26. A spring (not shown) urges the plate 22 towards the wall 20,whereby the plate 22 and the wall 20 comprise a capacitor 211 whosecapacity depends on the distance between the plate 22 and the wall 20.As the cylinder 10 rotates, the rod 12 moves in and out of the housing16 an amount depending on the difference between the maximum and theminimum diameters of the cylinder 10. The change in capacity of thecapacitor 21, and the change in the tuned frequency of the paralleltuned circuit comprising the capacitor 21 and the inductor 24 thereforedepends on the difference between the maximum and minimum diameters ofthe cylinder 10. The housing 14 is grounded as at 26.

The housing 114 and a junction of the inductor 24 and the capacitor 21are connected, respectively, to the outer 28 and to the inner 29conductor of a concentric conductor 30. The inner conductor 29 extendsto the anode of a diode 32. The inner conductor also extends by way of acapacitor 34 to an oscillator 36. The outer conductor 28 of theconcentric conductor 30 may be formed to shield the diode 32 and thecapacitor 34. The cathode of the diode 32 is connected to ground 26 byway of a load resistor 38 and a filter capacitor 39 in parallel.Therefore, as the cylinder rotates, a direct voltage which is positivewith respect to ground appears across the resistor 38, this voltagebeing of constant amplitude if the cylinder it) is perfectly cylindricaland this voltage varying in amplitude in such a manner that the maximumand minimum values of the voltage appearing across tl resistor 38 aremeasures of the maximum and minimum diameters of the cylinder 10.

The ungrounded terminal of the resistor 38 is connected to the inverting(ll) terminals of the differential amplifiers 40 and 42. The output ofthe differential amplifier 40 is connected to the base ofa NPNtransistor 44 whose emitter is connected to ground 26 and whosecollector is connected to the cathode of a diode 46. The anode of thediode 46 is connected to the input of a very high input impedance,relatively low output impedance noninverting amplifier 48. The anode ofthe diode 46 is also connected through a storage capacitor 50 to ground26, and to the collector of a PNP transistor 52. The emitter of thetransistor 52 is connected to the positive terminal 54 of a source ofpotential (not shown) whose negative terminal is connected to ground. ADump terminal 56 is connected to the input terminal of an invertor 5'?whose output terminal is connected to the base of the transistor 52. Theoutput terminal of the amplifier 48 is connected through a load resistor58 to one terminal of a differential amplifier 60 and directly to thenoninverting (NI) input terminal of the differential amplifier 40.

The output of the amplifier 42 is connected to the base of a PNPtransistor 62. The emitter of the transistor 62 is connected to thepositive terminal 54 of the source of potential (not shown). Thecollector of the transistor 62 is connected to the anode of a diode 64.The cathode of the diode 64 is connected to the input terminal of a veryhigh input impedance, low output impedance noninverting amplifier 66.The cathode of the diode 64 is connected to ground 26 through a storagecapacitor 68 and the cathode of the diode 64 is also connected to thecollector of a NPN transistor 70. The emitter of the transistor 70 isconnected to ground, and the base of the transistor 70 is connected tothe Dump terminal 56. The outpu erminal of the amplifier 66 is connectedthrough a load resistor 72 to the other input terminal of thedifferential amplifier 60. The output terminal of the amplifier 66 isconnected to the N] terminal of the differential amplifier 42. The twoinput terminals of the amplifier 60 are connected by an adjustabletolerance resistor 74.

The output of the differential amplifier 60 is connected to one of thetwo input terminals of an AND circuit 76, and by way of an invertor 78to one of the two input terminals of an Al I D circuit 80. The otherinput terminals of the AND circuits 76 and 80 are connected together andto a Read terminal 82. The, output terminal of the AND circuit 76 isconnected through an invertor 84 to a G0 signal device 86 and the outputterminal of the AND circuit 80 is connected through an invertor 88 to aNO GO signal device 90.

The operation of the described apparatus is as follows: The cylinder 10is rotated, and as noted above, a varying direct voltage which ispositive with respect to ground appears across the resistor 38. Toprepare the apparatus to give an indication of out-of-roundness of thecylinder 10, that is, to prepare the apparatus to indicate thedifference between the maximum and minimum dimensions thereof, apositive voltage with respect to ground is applied to the Dump terminal56 whereby the transistors 52 and 70 are both made conductive. Thecapacitor 50 is charged to a voltage which is higher than any voltageappearing across the resistor 38 from the source which is connected tothe terminal 54. The capacitor 68 is discharged to ground potential byway of the transistor 70. The positive potential on the terminals 56ceases. As long as the potential at the N! terminal of the differentialamplifier 40 is higher than the potential at the I terminal ofthisdifferential amplifier, a positive potential appears at the base of thetransistor 44, permitting the capacitor 50 to discharge through thediode 46. However, a voltage is fed back from the noninverting amplifier48 to the Ni input terminal of the differential amplifier 40 that is ameasure of the voltage across the capacitor 50. As the voltage on thecapacitor 50 goes down, the voltage applied to the NI input terminal ofthe differential amplifier 40 also goes down. A point will be reached inthe discharge of the capacitor 50 through the transistor 44 when thevoltage at the NI input of the differential amplifier 40 is equal to thelowest excursion of the voltage applied to the l input thereof, and atthis point, no potential or negative potential will be applied to thebase of the transistor 44, and the transistor 44 will cease to conduct.At this time, the voltage at the output of the amplifier 48 is equal tothe minimum voltage appearing across the resistor 38.

In a similar manner, as long as the voltage of the l input to thedifferential amplifier 42 is higher than the voltage at the NI input tothis differential amplifier 42, negative potential will be applied tothe base of the transistor 62 and the capacitor 68 will charge from thesource connected to the terminals 54 through the transistor 62 and thediode 64 to a value such that the voltage at the output of thenoninverting amplifier 66 is equal to the maximum voltage across theresistor 38. The application of the positive Dump signal to the terminal56 not only causes charging of the capacitor 50 and discharging of thecapacitor 68, but it also dissipates any stored voltages appearing onthese capacitors due to previous tests or measurements. The amplifiers48 and 66 have very high input impedances and therefore these amplifiersdischarge their respective storage capacitors 50 and 68 very slowly.When the transistors 44, and 70 have zero or reverse potentials on theirbases, their impedances are very high whereby they discharge theirrespective capacitors very slowly. Also when the transistors 52 and 62have zero or positive potentials on their bases, their impedances arevery high whereby they charge their respective capacitors very slowly.Therefore, the voltages at the output terminals of the amplifier 48 and66 are measures of the minimum and maximum diameters respectively oftherotating part 10.

The degree of accuracy to which the high and the low voltage across theresistor 38 are stored in the respective capacitors 68 and 50 is limitedonly by the open loop gain of the respective differential amplifiers 42and 40 and their input offset voltages. Therefore, with perfectdifferential amplifiers 42 and 40, the stored voltages on the capacitors68 and 50 would be perfect measures of the high and the low voltagesacross the resistor 38.

The differential amplifier 60 has a built in threshold. That is, as longas the difference in voltages applied to the two input terminals of thedifferential amplifier 60 is less than a predetermined amount, thedifferential amplifier 60 provides a positive output voltage. Therefore,if the difference between the small and the large diameters of thecylinder is such that the difference between the voltages applied to theinput terminals of the amplifier 60 is less than the said thresholdvalue thereof, the output of the differential amplifier 60 is positive.

This positive voltage is applied to one input terminal and the ANDcircuit 76 and is applied in an inverted phase to one input terminal ofthe AND circuit 80. When the difference in voltages applied to the twoinput terminals of the differential amplifier 60 is greater than thethreshold value thereof, the output thereof is negative. This negativevoltage is applied as negative potential to the said one input terminalof the AND circuit 76 and as positive potential to the said one inputterminal of the AND circuit 80. Upon applying a positive test pulse tothe Read terminals 82, that AND circuit 76 or 80 which has a positivevoltage at both of its input terminals will have a low voltage at itsoutput terminal and the appropriate signal device 86 or 90 will beoperated, due to the action of the respective invertor 84 or 88, toindicate that the voltage between the input terminals of thedifferential amplifier 60 is less than or greater than the built inthreshold value.

To permit adjustment of the tolerance of the described indicatingapparatus even though a tolerance is built into the differentialamplifier 60, the variable resistor 74 is provided. The value of theresistor 74 is adjusted so that the voltage across it is less than thebuilt in tolerances for any degree of difference in maximum and minimumdiameters of the cylinder 10 for which it is desired to produce a G0signal.

Modifications of the described dimension checking apparatus will occurto a person skilled in the art. Therefore the above description is to betaken as illustrative and not in a limiting sense.

What I claim is:

1. Apparatus for comparing two dimensions comprising,

a single transducer having an output voltage whose amplitude varies withtime, said amplitude having a maximum value representative of one of twodimensions and a minimum value representative ofthe other dimension,

a peak value detector circuit for providing a first DC voltagecorresponding to the maximum value ofsaid amplitude,

a minimum value detector circuit for providing a second DC voltagecorresponding to the minimum value of said amplitude,

threshold means having two input terminals and an output terminal whichprovides a first voltage output at its output terminal for all voltagesapplied to its input terminals whose difference is less than a thresholdvalue, and which provides a second voltage output on said outputterminal for all voltages applied to its input terminals whosedifference is greater than said threshold value,

means to apply said first and second DC voltages to the input terminalsrespectively of said threshold means, and

indicator means coupled to the output terminal of said threshold deviceto provide an indication of the output voltage of said threshold device.

2. The invention as expressed in claim 1 in which a variable resistor isconnected across the input terminals of said threshold means whereby thethreshold of said threshold means in combination with said resistor maybe varied.

3. Means for comparing two dimensions comprising means to store avoltage which is a measure ofthe smaller of the two dimensions,

means to store a voltage which is a measure of the greater of the twodimensions,

threshold means having two input terminals and an output terminal whichprovides a first voltage output at its output terminal for all voltagesapplied to its input terminals whose difference is less than saidthreshold value, and which provides a second voltage output on saidoutput terminal for all voltages applied to its input terminals whosedifference is greater than said threshold value,

means to apply respective voltages which are measures of the voltagesstored by said two storage means to the input terminals respectively ofsaid threshold means,

indicator means coupled to the output terminal of said threshold deviceto provide an indication of the output voltage of said threshold device,

said first-mentioned voltage-storing means comprising a capacitor, meansto charge said capacitor to a relatively high voltage, means todischarge said capacitor, a differential amplifier having a pair ofinput terminals and an output terminal, means to apply a voltage whichis a measure of the smaller of said dimension to one input terminal ofsaid differential amplifier, means to sense the voltage across saidcapacitor and means to apply a voltage to the other input terminal ofsaid differential amplifier which is a measure of the voltage sensed bysaid voltage-sensing means, and means to connect the output terminal ofsaid differential amplifier to said capacitor discharging means, wherebysaid capacitor is discharged until the voltage applied to one of theinput terminals of said differential amplifier is equal to the minimumvoltage applied to the other of said input terminals thereof.

4. Means for comparing two dimensions comprising means to store avoltage which is a measure of the smaller of the two dimensions,

means to store a voltage which is a measure of the greater of the twodimensions,

threshold means having two input terminals and an output terminal whichprovides a first voltage output at its output terminal for all'voltagesapplied to its input terminals whose difference is .less than saidthreshold value, and which provides a second voltage output on saidoutput terminal for all voltages applied to its input terminals whosedifference is greater than said threshold value,

means to apply respective voltages which are measures of the voltagesstored by said two storage means to the input terminals respectively ofsaid threshold means, and

indicator means coupled to the output terminal of said threshold deviceto provide an indication of the output voltage of said threshold device,

I said second voltage storage means comprising a capacitor,

means to charge said capacitor, ,a differential amplifier having a pairof input terminals and an output terminal, means to apply a voltagewhich is a measure of said greater dimension to one input terminal ofsaid difterential amplifier, means to sense the voltage across said

1. Apparatus for comparing two dimensions comprising, a singletransducer having an output voltage whose amplitude varies with time,said amplitude having a maximum value representative of one of twodimensions and a minimum value representative of the other dimension, apeak value detector circuit for providing a first DC voltagecorresponding to the maximum value of said amplitude, a minimum valuedetector circuit for providing a second DC voltage corresponding to theminimum value of said amplitude, threshold means having two inputterminals and an output terminal which provides a first voltage outputat its output terminal for all voltages applied to its input terminalswhose difference is less than a threshold value, and which provides asecond voltage output on said output terminal for all voltages appliedto its input terminals whose difference is greater than said thresholdvalue, means to apply said first and second DC voltages to the inputterminals respectively of said threshold means, and indicator meanscoupled to the output terminal of said threshold device to provide anindication of the output voltage of said threshold device.
 2. Theinvention as expressed in claim 1 in which a variable resistor isconnected across the input terminals of said threshold means whereby thethreshold of said threshold means in combination with said resistor maybe varied.
 3. Means for comparing two dimensions comprising means tostore a voltage which is a measure of the smaller of the two dimeNsions,means to store a voltage which is a measure of the greater of the twodimensions, threshold means having two input terminals and an outputterminal which provides a first voltage output at its output terminalfor all voltages applied to its input terminals whose difference is lessthan said threshold value, and which provides a second voltage output onsaid output terminal for all voltages applied to its input terminalswhose difference is greater than said threshold value, means to applyrespective voltages which are measures of the voltages stored by saidtwo storage means to the input terminals respectively of said thresholdmeans, indicator means coupled to the output terminal of said thresholddevice to provide an indication of the output voltage of said thresholddevice, said first-mentioned voltage-storing means comprising acapacitor, means to charge said capacitor to a relatively high voltage,means to discharge said capacitor, a differential amplifier having apair of input terminals and an output terminal, means to apply a voltagewhich is a measure of the smaller of said dimension to one inputterminal of said differential amplifier, means to sense the voltageacross said capacitor and means to apply a voltage to the other inputterminal of said differential amplifier which is a measure of thevoltage sensed by said voltage-sensing means, and means to connect theoutput terminal of said differential amplifier to said capacitordischarging means, whereby said capacitor is discharged until thevoltage applied to one of the input terminals of said differentialamplifier is equal to the minimum voltage applied to the other of saidinput terminals thereof.
 4. Means for comparing two dimensionscomprising means to store a voltage which is a measure of the smaller ofthe two dimensions, means to store a voltage which is a measure of thegreater of the two dimensions, threshold means having two inputterminals and an output terminal which provides a first voltage outputat its output terminal for all voltages applied to its input terminalswhose difference is less than said threshold value, and which provides asecond voltage output on said output terminal for all voltages appliedto its input terminals whose difference is greater than said thresholdvalue, means to apply respective voltages which are measures of thevoltages stored by said two storage means to the input terminalsrespectively of said threshold means, and indicator means coupled to theoutput terminal of said threshold device to provide an indication of theoutput voltage of said threshold device, said second voltage storagemeans comprising a capacitor, means to charge said capacitor, adifferential amplifier having a pair of input terminals and an outputterminal, means to apply a voltage which is a measure of said greaterdimension to one input terminal of said differential amplifier, means tosense the voltage across said capacitor and means to apply a voltage tothe other input terminal of said differential amplifier which is ameasure of the voltage sensed by said voltage-sensing means, and meansto connect the output terminal of said differential amplifier to saidcapacitor-charging means, whereby said capacitor is charged until thevoltage applied to one of the input terminals of said differentialamplifier is equal to the maximum voltage applied to the other of saidinput terminals.